Objects to be weighed, such as detergents and confectionery, which have been weighed to have specified weight by a combination weigher, are typically packaged by a packaging machine. A schematic construction of a first conventional example of such a combination weigher which weighs the objects to be weighed is shown in FIG. 13.
The combination weigher of FIG. 13 is configured such that a control unit 30 controls an operation of the entire combination weigher and performs combination calculation. The combination weigher is constructed in such a manner that a center base body (body) 11 is disposed at a center of the combination weigher, and a dispersion feeder 1 having a conical shape is mounted to an upper part of the center base body 11 to radially disperse objects to be weighed supplied from an external supplying device by vibration. Around the dispersion feeder 1, linear feeders 2 are provided to transfer the objects to be weighed which have been sent from the dispersion feeder 1 into respective feeding hoppers 3 by vibration. A plurality of feeding hoppers 3 and weighing hoppers 4 are disposed below the linear feeders 2 and are arranged in a circular shape in such a manner that each feeding hopper 3 and each weighing hopper 4 correspond to the associated one of the linear feeders 2. The feeding hopper 3 receives the objects to be weighed which have been sent from the linear feeder 2, and opens its gate to feed the objects to be weighed to the weighing hopper 4 located therebelow when the weighing hopper 4 becomes empty. The weighing hopper 4 is attached with a weight sensor 41 such as a load cell. The weight sensor 41 measures weight of the objects to be weighed inside the weighing hopper 4. The control unit 30 performs combination calculation to determine a combination made up of hoppers which will discharge the objects to be weighed, from the plurality of weighing hoppers 4. The weighing hoppers 4 corresponding to the combination discharge the objects to be weighed onto a collecting chute 12. The collecting chute 12 is disposed below the weighing hoppers 4. The objects to be weighed which have been discharged from the weighing hoppers 4 slide down on the collecting chute 12 and are held in a collecting hopper 13 provided at a discharge outlet in a bottom part of the collecting chute 12. Thereafter, the objects to be weighed are sent out to a packaging machine which is not shown. While manufacturing package bags, the packaging machine charges the objects to be weighed which have been discharged from the combination weigher into the package bags and packages them.
In order to enable the combination weigher to be adapted to a high-speed operated packaging machine, it is necessary to provide a collecting hopper 13 at a discharge outlet of the collecting chute 12 so that the objects to be weighed are discharged in a state where they are lumped together, and to shorten a discharge cycle time. To this end, conventionally, the number of weighing hoppers was increased to a certain degree to configure so that a double shift operation is carried out rather than a single shift operation, thereby reducing the discharge cycle time taken for the single shift operation by half. The single shift operation is carried out in a configuration in which, for example, a total number of the weighing hoppers 4 is set to ten, the number of the weighing hoppers 4 selected to make up of a combination is set to four, the combination calculation is performed once within one weighing cycle time, the weighing hoppers 4 perform discharge operation once within one weighing cycle time, and the collecting hopper 13 performs discharge operation with respect to the packaging machine once within one weighing cycle time. In order to achieve weighing precision substantially as high as that in the single shift operation when the double shift operation is carried out, the number of the weighing hoppers 4 is increased by four so that a total number of them is fourteen and the number of the weighing hoppers 4 selected to make up of the combination is set to four. And, the combination calculation is performed once in every ½ of one weighing cycle time, weighing hoppers 4 making up of a combination selected in the combination calculation discharge the objects to be weighed, and according to the discharge, the collecting hopper 13 discharges the objects to be weighed. That is, the combination calculation is performed twice within one weighing cycle time, the weighing hoppers 4 performs the discharge operation twice within one weighing cycle time, and the collecting hopper 13 performs the discharge operation with respect to the packaging machine twice within one weighing cycle time. This makes it possible to improve productivity within a specified time period (the total number of times the combination weigher discharges the objects to be weighed to the packaging machine) and hence to adapt the combination weigher to the high-speed operated packaging machine.
However, even when the conventional combination weigher shown in FIG. 13 is configured to carry out the double shift operation, a batch length of the objects to be weighed which have been discharged from the weighing hoppers 4 and slide on the collecting chute 12 is not reduced. For this reason, a distance between the batches of the objects to be weighed discharged from the weighing hoppers 4 selected to make up of a previous combination and the objects to be weighed discharged from the weighing hoppers 4 selected to make up of a subsequent combination is insufficiently large and the objects to be weighed in the previous and subsequent combinations are likely to be mixed, making it difficult to carry out the double shift operation at a specified operation speed. To solve this problem, two collecting chutes may be provided as shown in FIG. 14.
FIG. 14(a) is a schematic partial cross-sectional view showing a second example of the conventional combination weigher as viewed from laterally. FIG. 14(b) is a schematic view of collecting chutes (inner chute and outer chute) and weighing hoppers of the combination weigher as viewed from above. The combination weigher is configured in such a manner that a lower chute is incorporated into the combination weigher disclosed in a patent document 1 to discharge objects to be weighed into a packaging machine having one inlet.
In the combination weigher, two collecting chutes, i.e., an inner chute 6 and an outer chute 7 are provided, and each weighing hopper 4 has two gates (not shown) to be able to discharge objects to be weighed selectively to the inner chute 6 or the outer chute 7 which is located therebelow. In addition, a collecting hopper 8 is provided at an discharge outlet 6e in a bottom part of the inner chute 6 to hold and discharge the objects to be weighed, and a collecting hopper 9 is provided at an discharge outlet 7e in a bottom part of the outer chute 7 to hold and discharge the objects to be weighed. Furthermore, one lower chute 10 is provided below the two collecting hoppers 8 and 9 to feed the objects to be weighed which have been discharged from the collecting hoppers 8 and 9 into one inlet of the packaging machine. A control unit 31 controls an operation of the entire combination weigher and performs combination calculation. The combination weigher is configured to carry out the double shift operation in such a manner that the weighing hoppers 4 selected sequentially to make up of the combinations discharge the objects to be weighed alternately to the inner chute 6 and the outer chute 7 and the collecting hopper 8 and the collecting hopper 9 alternately discharge the objects to be weighed to the lower chute 10. Thereby, the objects to be weighed are discharged twice from the discharge outlet 10e of the lower chute 10 within one weighing cycle time. So, productivity within a specified time period can be improved. Also, since the weighing hoppers 4 discharge the objects to be weighed to each of the inner chute 6 and the outer chute 7 only once within one weighing cycle time, a sufficient distance is provided between the batches of the objects to be weighed which are discharged previously and the objects to be weighed which are discharged subsequently on each of the chutes.
In cases where the combination weigher is not equipped with the lower chute 10, two packaging machines or a twin-inlet packaging machine having two inlets are/is disposed below the combination weigher, and the objects to be weighed which have been discharged from the collecting hoppers 8 and 9 are fed into the associated packaging machine inlets. In this case, by the double shift operation, the objects to be weighed are discharged once to each of the two packaging machine inlets within one weighing cycle time. That is, the objects to be weighed are discharged twice in total within one weighing cycle time irrespective of the presence or absence of the lower chute 10. Thus, productivity within a specified time period can be improved.
Patent document 1 Japanese Laid-Open Patent Application Publication No. Sho. 57-125322
Patent document 2 Japanese Examined Patent Application Publication No. Hei. 8-1395